Question 1

What are Node streams and why use them?

Accepted Answer

Streams process data in chunks with backpressure, avoiding loading entire payloads into memory. Readable/Writable/Duplex/Transform cover pipelines for HTTP, files, and transforms. Essential for large uploads, proxies, and ETL. Misusing streams (buffering everything) defeats the purpose.

Question 2

Explain backpressure in Node streams.

Accepted Answer

When a writable cannot keep up, it signals the readable to pause — write returns false and 'drain' resumes. Ignoring backpressure causes unbounded memory growth. Prefer pipeline/pipelinePromise over manual pipe for error propagation. Interviewers love 'what happens if producer is faster than consumer?'

Question 3

pipe vs pipeline — which should you use?

Accepted Answer

stream.pipeline (or pipelinePromise) handles errors and cleanup; classic pipe does not auto-destroy on error. Always prefer pipeline in new code. Unhandled stream errors are a common crash source. Attach error handlers if you must use pipe.

Question 4

How do you implement a Transform stream?

Accepted Answer

Extend Transform and implement _transform(chunk, enc, cb) (and optionally _flush). Push transformed chunks, handle errors via callback, respect objectMode when needed. Keep transforms pure and fast; heavy work belongs off-thread.

Question 5

Debugging: memory grows while streaming a large file upload. Likely causes?

Accepted Answer

Buffering entire body, missing backpressure, collecting chunks into an array, or not consuming the stream. Ensure upstream pauses correctly. Avoid await req.arrayBuffer() for huge bodies. Stream to disk/object storage. Watch for multiple consumers.

Question 6

Architecture: design a high-throughput log shipping agent in Node.

Accepted Answer

Readable from sources â†’ transform (parse/enrich) â†’ writable to sinks with pipeline, bounded queues, and retry/backoff. Use objectMode carefully. Separate CPU-heavy parse to workers. Expose metrics for lag, drop rates, and backpressure events. Prefer proven agents if ops maturity is low.

Streams Node.js Interview Questions

Other Node.js interview topics